Brownfieldsare abandoned or underused industrial and commercial facilities available for re-use. The land may be contaminated by low concentrations ofhazardous wasteorpollution, and has the potential to be reused once it is cleaned up. Land which is severely contaminated and have high concentration of pollution can not be reused. This assignment deals with the site contamination and the remedial measure taken to make it reusable. On the next part shear testing and chemical testing of soil is done.
Brownfield sites are those areas which are abandoned and unused but can be reused. There can be many causes and types of site contamination:-
* Industrial Pollution
* Mines and factories as pollution source
* Agriculture pollution from farms and machinery
* Fly tipping
* Miscellaneous Pollution
We will discuss these causes one by one.
The contaminants found on urban brownfield sites can be of three kinds:
construction debris, petrochemical contaminationfrom transport and fuels andheavy metals and chemicals. In many buildings constructions asbestos is widely used as it has very good sound insulation properties as well as heat retention properties. Asbestos has been used quite a lot in ceiling tiles and noise absorption tiles. Due to these properties gymnasium hall and concert hall have asbestos in their ceiling.Asbestos is safe to human body except when it is cut or burnt. It's when the particles are airborne that they are the most dangerous. Presence of asbestos can cause Cancer in human beings.
Mines and Factories as Pollution source
Mine works is an important source of landpollution. Heavy metals such as cadmium, lead and copper may be deposited in unsafe amounts, locally. Some of these toxic metals accumulate over a period of time. Some deposits may take thousands of years to vanish naturally to safe levels. Unsafe and mismanaged metal recycling facilities can also account for land contamination.
Farms can also cause landpollutionby allowing manure to accumulate and percolate into nearby ground. Chemicals used in sheep dipping have also caused serious implications on land. Diesel oil spills are a very common danger. Modern farming also gives rise to a lot of waste material such as plastic wrapping for silage, used pesticide containers, old tires, batteries andused up machinery.One major cause of landpollutionis agricultural run-off from fertilizers. They can create havoc in the eco-system by causing eutrophication, which is increase in concentration of chemicals, which ultimately leads to destruction of ponds and lakes.(Evan nye, 2001). Herbicides and pesticides can also remain in soils and accumulate in the bodies of living organisms and ultimately ending up in food chain.
Litteringandfly-tippingby informal traders of waste and individuals can be a cause of land pollution. Consumer products such as computers and old appliances contain hazardous components which need careful and controlled disposal methods. So when traders and individuals take short cuts to solve their waste problem, land gets polluted. According to the UK Environment Agency, asbestos,a household wasteandused in vehicle partsis the most common waste materials found at pollution incidents.(Evan nye, 2001)
Miscellaneous causes of Pollution
The large amounts of refuse due to overcrowding, informal settlements such as shanty towns and poorly maintained sewage pipesare can be causes of landpollutionin many developing countries. Human sewage is not generally a problem in developed nations but they are main concern in developing countries. Pollution can also be a cause in landfill sites where leachates(polluted liquids) ooze out into neighboring land.(Ginn, 1996) These hazardous liquids elements pollutelocal water sources. The sites such as graveyards are also contaminated by cholesterol and amyloid which are present in human remains.
Some Considerable Abbreviations: -
* CLEA: Contaminated Land Exposure Assessment.
* SGV: Soil Guidelines Values.
* EQS: Environmental Quality Standards.
* EIA: Environmental Impact Assessment.
* IPPC: Integrated Pollution Prevention and Control.
* WFD: Water Framework Directive.
Generic Risk Assessment
Generic screening values are compared to soil and groundwater results, e.g. CLEA SGVs for soils and EQS or UK Drinking water standard for waters.
Land restoration is when brownfields are “cleaned up” to make them usable for other projects. Redeveloping a brownfield means removing harmful chemicals and components, which leads to improved air, water, and soil quality. There are various environmental and economical benefits. Such as increased land preservation as more and more brownfields sites get cleaned and reused, resulting in less urban sprawl. Redeveloped brownfields have been vastly used for a range of establishments, including commercial properties, residential neighborhoods, and green spaces. (Ginn, 1996)
For the site to be made free from contamination a site evaluation or investigation should be conducted for purposes of determining the extent, of contamination on a property. An assessment of contamination can be informal or formal, and can consist of several stages. For example, a Phase I assessment includes basic study of possible contamination at a site, in which information is collected about the past and present usage of site and present conditions are inspected throughly. Phase II assessment follows Phase I assessment with where sampling and analysis of suspected contaminated areas of a site is done. A Phase III assessment is either follow up by a Phase II assessment by gathering information on the exact extent of the contamination or by preparing plans and remedies for site cleanup. In some cases, the contamination is localized and it is better to “cap” it than disturb it in an attempt to remove it.
Conventional Methods of remediation used are:-
* Do nothing.
* Dig and Dump.
* Soil washing.
* Thermal treatment.
In this the contaminated site is kept as such over a period of time. Appropriate measure are needed for controlling the further contamination of site.
Dig and Dump
This is used for small scale sites. In these cases the actual movement of waste may prove expensive. The cost of waste to be filled varies from £ 32 per ton to £ 250 per ton.
This is also known as soil mixing. This is a method in which the soil is mixed with grout mortar so as to make it inert. This is done to prevent it from reacting with any toxicants and contaminants. Grout is basically a construction material used to embed rebars in masonry walls, fill voids, and seal joints. Grout is generally a mixture of water, cement and sand.
They are used as a pre or post treatment process. In this method the contaminated soil is treated with chemical reagents. This is done to separate the contaminants from the soil it includes thre types of chemical processes: -
It uses water to remove contaminants from the soil. Water being the universal solvent makes this method most popular and economical. In this method the contaminants are washed out of the soil by scrubbing the soil. After scrubbing we get two separate parts of the soil, one cleaned and other polluted.
In this the contaminated soil is heated which burns off the chemicals or create extractable vapour.
At different temperature different contaminants get vaporized and extracted.It is expensive than most of the treatments.
Innovative remedial techniques that can be used at brownfields are:-
* In situ oxidation
* Soil vapor extraction
* Miscellaneous Techniques
Bioremediationcan be defined as any process that usesmicroorganisms,fungi,green plantsor theirenzymesto return the natural environment altered by contaminants to its original condition. Bioremediation may be employed to attack specificsoil contaminants, such as degradation ofchlorinatedhydrocarbonsbybacteria. An example of a more general approach is the cleanup ofoil spillsby the addition of nitrateand/orsulfatefertilizersto facilitate the decomposition ofcrude oilby indigenous or exogenous bacteria. There are a number of cost/efficiency advantages to bioremediation, which can be employed in areas that are inaccessible withoutexcavation.For example hydrocarbon spills or certain chlorinated solvents may contaminategroundwater and treatment using this method is much cheaper than using methods such as in situ oxidation. (Evan nye, 2001)
In Situ Oxidation
In situ chemical oxidation(ISCO) is an efficient and environmentally safe cleanup technique used to treat soil or groundwater by reducing the concentrations of targeted environmental contaminants to acceptable levels. ISCO is done by introducing strong chemical oxidizers directly into the contaminated medium (soil or groundwater) to destroy chemical contaminants in that medium. It can be used to treat a variety of organic compounds, including some which are resistant to natural degradation. (Ginn, 1996) The effectiveness of the oxidation is dependent on the site lithology, the amount of oxidant used, the residence time of the oxidant, the degree of effective contact between the oxidant and the contaminant and the presence of oxidizing materials other than the targeted contaminants.
Soil Vapor Extraction
Soil vapor extraction(SVE) is an effective remediation technique for soil purification. SVE utilizes different technologies to treat the volatile organic compounds (VOCs) generated after vacuum removal of air and vapors from surface. This technique incorporates granular activated carbon thermal or catalytic oxidation and vapor condensation. Generally, carbon is used for low (<500ppmV) VOC concentration vapor streams, oxidation is used for moderate (up to 4,000 ppmV) VOC concentration streams, and vapor condensation is used for high (>4,000 ppmV) VOC concentration vapor streams.
Phytoremediation refers to the natural ability of certain plants known as hyper accumulators to bio accumulate, degrade or remove harmless contaminants in soils, water or air. Contaminants such as metals, pesticides, solvents, explosives, crude oil and its derivatives have been removed by this method so far in various parts of world. Many plants such as alpine pennycress, mustard plants and pigweed have proven to be very successful at hyper accumulating contaminants. Phytoremediation is a clean, cost-effective and environmentally supportive technology, as opposed to mechanical cleanup methods such as soil excavation or pumping polluted groundwater.
Mycoremediationis a form ofbioremediation, the process of usingfungito return anenvironment contaminated bypollutantsto a less contaminated state. One of the primary roles offungiin theecosystemisdecomposition, which is performed by the mycelium. When hydrocarbons such as diesel come in the contact of these fungi it breaks it into non toxic compounds.(Evan nye, 2001)
Xenocatabolismis aconceptinbioremediation according towhich there are certain microbes,which feed on substances such asamyloid,cholesteroland other related substances in places that are full ofhumanremains, such asgraveyards. The biomedicalapproach would be to identify the genetic basis for their generous satiate capacity, and to put one or twogenesinto human beings, thereby enhancing our own ability to break things down, and to thereby get rid of things that we cannot naturally break down. This concept is under development.
Impact of remediation work
The Brownfield site, utilization is an increasingly important element of sustainable spatial development. The redevelopment of Brownfield sites helps reduce the impact of urban sprawl and the demand to develop on valuable Greenfield space. Brownfield sites are present in most cities and so is an issue for most people. When viewed as opportunity sites and effectively regenerated the potentials of Brownfield sites can be realized. They can enhance the quality of the urban environment, attract people to live and spend time in the city and thus boosting the economy, instill a sense of pride in the city's inhabitants and protects and enhances the city's heritage.
Brownfields can be found in communities large and small, urban and rural. Brownfields are often situated in key areas throughout the community, such as downtown or along the waterfront. The key to this property lies in their value- not only there monetary value, but the cultural heritage and social value as well. For instance, a building or structure on brownfield property may have cultural value because it's an example of an early type of construction or it's associated with an event which is significant to the community. The redevelopment of brownfield properties can also increase community pride, encourage economic investment and contribute to health and vitality of a community.
Brownfeilds are strategically located sites and form important part of economic land supply. Reusing brownfields properties bring sustainable communities by effectively redirecting growth, preserving green space and ensuring wise management of land and other resources. As more brownfield sites are located within the city core, redevelopment makes use of existing transit and other public infrastructure, reducing investment cost. The community benefits as a whole with the added economic activity and increase in municipal tax revenue.
In addition to providing benefits to surrounding communities, property owners that clean up and reuse their brownfield sites may benefit directly by:
* They can avoid any environment enforcement actions by sate and local regulatory agencies, which could result in penalties.
* They can also receive tax exemptions regarding reuse and cleaning of property.
* By doing the cleaning they reduce the likelihood of contamination of groundwater under the site, thereby checking liability and long term costs of cleaning up the property;
* Creating good will within the community
* By regulating site contamination they can realize an enhanced return from the property, by making it more valuable and marketable.
Shear Strength Measurement
Shear strength is the maximum strength of the soil at which significant deformation or yielding occurs due to applied shear stress. The safety of any structure depends upon the shear strength of the soil on which it is made. If the soil fails, then the structure can also collapse. The study of shear strength is also important to make earthquake resistant buildings.
Factors influencing shear strength
* Soil composition.
* State: - Defined by the ratio of effective normal stress and shear stress.
* Structure: - Defined by arrangement of particles within the soil mass.
* Loading Conditions
Determination of Shear stress
There are two methods to determine Shear stress viz.
* Direct Shear Test
* Triaxial Shear Test
Direct Shear Test
We will get our desired results from Direct shear Test. It can be used to determine the shear stress of both cohesive as well as non cohesive soils. This test is quick and rather cheap. The main drawback of this method is that it fails the soil on the designated plane which may not be the weakest one.The test equipment consists of a metal box into which a soil specimen is placed. Vertical force is applied through metal platen. Shear force is applied by moving one half of the box relative to each other causing failure in the soil specimen.
Direct Shear Strength Measurement Procedure
Measure the diameter of the inner box and find the area.
Make sure the top and bottom half of the shear box in contact and fixed together.
Weigh out 150 gm of sand.
Place the soil in three layers in the mould using funnel. Compact the soil with 20 blows per layer.
Place cover on the top of the sand.
Place Shear box on the machine.
Apply normal force. The weights to use for the three runs are 2 kg, 4 kg and 6 kg if the load is applied through a lever arm or 10 kg, 20 kg and 30 kg, if the load is applied directly.
Start the motor at selected speed so that the rate of shearing is at a constant rate.
Take the horizontal displacement gauge, vertical displacement gage and shear load gage reading. Record the reading on the data sheet.
Continue taking readings until the horizontal shear load peaks and then falls, or the horizontal displacement reaches 15% of the diameter.
Lever arm ratio = 1:10.
Determine the Dry Unit Weight as ‘'
Calculate the Void Ratio as ‘e'
Calculate the Shear stress and Normal stress as ‘σ' and ‘τ' respectively.
1. Sample one is clean and not contaminated 16 Kg and Load at failure was 87.5 N
2. Sample two contaminated with fuel Ash and , 8 Kg and load of failure at 29.1.
* Soil Pollution Origin, Monitoring and Remediation, Mirsal, Ibrahim A, 2008.
* Practical handbook of soil, vadose zone, and ground-water contamination, Russell Boulding, Jon S. Ginn, 1996.
* Assessment of soil contamination – a functional perspective, NicoM.van Straalen, 2002.
* Practical techniques for groundwater and soil remediation, Evan K. Nye, 2001
* www.egr.msu.edu/classes/ene802/soil_washing.ppt, accessed on 22 nov 2009.
* http://www.brownfieldscenter.org/big/faq.shtml, accessed on 23 nov 2009.